1. Field of the Invention
The present invention relates to a proximity detector for sensing the presence of a conducting or other high dielectric object and, more particularly, to a proximity detector utilizing a negative resistance oscillator circuit in a manner in which oscillation occurs only in the presence of an object which can be sensed.
2. Description of the Prior Art
The prior art is replete with many types of proximity sensing devices. These include devices employing conventional oscillators wherein the oscillating condition of the oscillator in the proximity switch is changed somewhat by the electrostatic capacity produced by the approach of an object to be sensed. For example, the oscillator may be de-energized, its oscillation frequency changed or the like. Because of the operating characteristics of many of such systems, the signals produced by the approach of an object of interest are smaller than desired and often quite difficult to recognize without sophisticated circuitry associated with the device.
This reduces the reliability of the device or greatly increases the cost. One such device is illustrated and described in a patent to Tanaka et al, U.S. Pat. No. 4,030,037 issued June 14, 1977, which illustrates and describes a continuously oscillating system which detects the proximity of an object of interest such as, for example, a human body by a circuit imbalance which reverses the polarity of the input to a differential amplifier in the system. For some objects, however, the signal may be too weak to produce the required polarity reversal. Thus, there remains a need for a simple, low cost, sensitive proximity detecting device.